IgE is the major class of antibody mediating immediate hypersensitivity, in that allergic responses are associated with elevated levels of IgE antibodies specific for certain allergens. In order to understand the basis of human allergic diseases, it is important to elucidate how IgE antibody production is regulated and how IgE functions in mediating hypersensitivity reactions. This research program proposes a detailed analysis, applying recombinant DNA technology, of the structure of IgE heavy (Epsilon) chain gene and its expression and the structure of IgE protein as related to its function. First, attention will be directed to a population of B cells, precursors of IgE-producing plasma cells, which have both IgM and Ig E determinants on the surface (Mu+ Epsilon+). We believe delineation of the nature of these cells is a key to understanding the regulation of IgE synthesis. Unlike IgE-producing plasma cells in which a class switching event has taken place at the Ig gene locus so that the VH sequence is expressed on the Epsilon chain, in Mu Epsilon cells the CEpsilon gene may not be rearranged but may be selectively activated among other CH genes so that the CEpsilon polypeptide (not the complete Epsilon chain) is expressed on the cell surface. This hypothesis will tested by studying the activity of the CEpsilon RNA transcripts and detecting CEpsilon polypeptides. Second, the DNA sequence 5 feet to the CEpsilon gene which may be important for the regulation of CEpsilon gene expression will be analyzed. This region contains, in addition to the already identified SEpsilon gene, a transcription initiation region if the model proposed above is correct. The transcription initiation region will be identified and sequenced and the role of the SEpsilon region in controlling IgE production will be established. Third, the structure-function relationship of the IgE molecule will be established. Areas on the Epsilon chain responsible for the various activities of IgE will be studied by DNA recombination and DNA-mediated gene transfer, expression of cloned cDNA in E. coli, oligonucleotide-directed site-specific mutagenesis and synthetic peptides. The long-term goals of this research are: 1) establishment of a precise knowledge of the intricate network of genetic, cellulr and molecular components involved in the regulation of IgE production; and 2) the development of methods or agents for the treatment of human allergic disorders.